Fastener



May 2 1939' c. G. oLsoN -f 2,156,350- y FASTENER Filed April 19, 193'? Patented May 2,1939

PATENT OFFICE FASTENER Carl G. Olson, Chicago,

Tool Works, Chicago, Ill.,

Illinois Ill., assignor to Illinois a corporation of Application April 19, I1937, Serial No. 137,721

10 Claims..

This invention relates generally to fasteners, and more particularly to fasteners of the selftapping type.

It is an important object of the present invention to provide ina screw designed to cut its own thread in relatively hard material, a cutting edge which is more effec-tive in cutting away material than cutting edges of commercial screws with which I am familiar.

More specically, the invention contemplates the provision of a cutting edge which is relatively sharp and to this end I propose tov provide a screw body with a novel recess arrangement.

Still more specically, this invention contemv plates a self-tapping screw, as above setforth, in which one section of the screw'disposed adjacent a longitudinally extending recess is adapted to yield toward a rigid section provided with a relatively sharp serratedcutting edge.

The foregoing and other objects and advantages will be more apparent from the following detailed description when considered in connection with the accompanying drawing, wherein- Figure 1 is a side elevational view of a selftjapping screw embodying features of my invenion;

Figure 2 is a bottomend elevational view of the screw body shown inl Figure 1 to more clearly illustrate the arrangement of the lonigtudinally extending recess;

Figure 3 is a diagrammatic representation of the entering end of the screw-to more clearly illustrate the acute cutting edge provided onthe screw which is constructed in accordance with o the teachings of the present invention;

Figure 4 is a fragmentary longitudinal sectional viewof the screw taken substantially along the line 4-4 of Figure 1; and

kFigure 5 is a screw embodying features of the present invention, said screw having a thread arrangement at ther entering end which structurally diiers from the screw shown in Figure 1.

Referring now to the drawing more in detail wherein like numerals have been employed toA designate similar, parts throughout the various views, it will be seen that one embodiment of my invention is represented by a self-tapping screw designated generally by the numeral I0 in Figure 1. This screw is provided with any suitable type of head l2 which, in the present embodiment, is of the hexagonal washer head type. Formed integral with the screw head l2 is a threaded body portion i4. In the disclosed embodiment the thread on the body' lli extending along the portion indicated by the bracket A is of a convenend of the screw,

' thread on the holding portion A the work. While screws (Cl. 85-47l tional machine screw type and is of constant height and crest diameter. By conventional machine screw type I mean the standard or usual V-shaped threads which are commonly referred to by the trade and in handbooks as machine 5 screw type threads. The thread convolutions embraced by the bracket I3- decrease in external diameter, but conform'in cross sectional contour with the corresponding portions of the thread convolutions on the holding portion A. The por- 10 tion B is the thread-forming or tapping portion and is provided with the decrease in crest diameter to facilitate initial application thereof to the unthreaded aperture of a work piece.

The axial pitch of the crest of the thread on 15 both the holding and tapping portions is uniform and the crown of the thread convolutions is uniform throughout the entire length of the screw.

In the screw embodiment shown in Figure 1, exposed peripheral core portions i6 are presented '20 which increase in axial width toward the entering said core portions conforming in diameter to the constant root diameter of the Particular attention is directd to a longitudinal recess indicated generally bythe numeral I8. This recess l-is comprised `of two recess sections I8a and `Iilb and is positioned to one side of the screw axis in order to render a section 20 of the screw yieldable. screw is substantially rigid and the onlyvpurpose in providing the recess section I8b is to increase the acuteness, of the serrated cutting edge 2l ex-' tending along the rigid screw section 22.

When the screw is initially applied to the unthreaded aperture of a work piece, the section 20 yields toward the section 22 and in this manner increases the cutting eectiveness of the cuttingedge 24. Employing the recess section lBb, the angularity of the cutting edge is increased from the substantially rightangle indicated by the letter C in Figure 3 to an acute angle represented by the letter D in Figure 3. This increased v sharpness of the cutting edge materially enhances the cutting effectiveness of the screw in having cutting edges of the angularity indicated by the letter C (Figure 3) arevery'pIactical and satisfactory when used in most materials, it has been found that such screws do not cut as freely in certain other materials, such as ber or substances made of compressed cloth, et cetera. As an example of such material, I call attention to cloth compositions used with a suitable binder such as shellac and other reslnous materials. By having the screw 'Ihe opposite section 22 ofthe 30 provided with the acute angle D, sumcient increase in cutting effectiveness is obtained to render the screw freely insertable within fibrous and other similar materials.

The recess I8 may be referred to as a stepped slot for the reason that the shallower recess I8b provides a step Isc., I prefer to form the recess I8 by the use of rotary cutters, the radii of which are indicated in Figure 4. The cutter used in forming the recess section I8a has a larger radius than the cutter employed to form the recess section lsb. By making the recess section`l8b relatively shallow, the rigidity of the screw section 22 is maintained and this is desirfable from the standpoint of satisfactory functioning. In the slotting of these screws I am able to employ two adjacently positioned cutters which rotate together as a unit and this method of procedure can be carried out in a very satisfactory and economical manner.

In Figure 5 a slightly modified tapping screw, designated generally by the numeral |011, is shown, and this' screw is provided with a conventional head Ib formed integral with a threaded body Mb. The screw Illa. is provided -With a recess i8 which is identical with the recess I8 previously described in connection with the longitudinal recess,

screw I0. The srew IDa differs from the screw I0 in that the thread on the tapping portion is constant in height, although the crest diameter thereof decreases toward the entering end of the screw. l

From the foregoing it will be apparent that by employing the novel recess arrangement described herein, the cutting effectiveness and the consequent practical utility of the screw is mate-A rially enhanced. Conventional machine shop methods may be employed in the manufacture of the screw with the utmost economy and speed. The recess is so disposed as to expedite the disposition of chips formed during the cutting operation. The increase in width at the periphery affords more space to receive the chips, and the curved bottom surfaces or walls of the recesssections serve to direct the chips axially of the screw. Obviously the invention is not limited to the particular type of tapping screw disclosed herein, but is capable of numerous other applications and modifications, said invention being limited only 'by the scope of the appended claims. Having thus Vdescribed my invention, what I claim as -new and desire to'secure by Letters Patent is:

1. A thread cutting fastener including a body portion provided with a thread, said body por tion being divided into a pair of sections by a longitudinal recess, said recess comprising .two communicating recess portions of diering depths, one vof'said sections being positioned adjacentl the recess portion of less depth and having' a cutting edge and the other section being yieldable forrincreasing the cutting effectiveness off 'the -edge on said first mentioned section.

' 2. A thread Acutting fastener including a body portion provided with a thread, said body portion being. divided into a pair of sections by a said recess having parallel side walls, one `of said sections having an acute serrated cutting edge at the entering end of the fastener and the other section 'being yieldable for increasing the cutting effectiveness of ther edge on said rst mentioned section, thread con- -volutions decreasing in external diameter toward the entering end of the fastener to facilitate annesso application thereof to an unthreaded aperture in a work piece.

3. A tapping fastener including a body portion provided with -a thread, said body portion being divided into a pair of sections by a longitudinal stepped recess, saidv recess providing an acute cutting edge on the section adjacent the shallower step which is adapted to cut away material when the fastener is turned within an unthreaded aperture of a work piece.-

4. A tapping fastener including a body portion provided with a thread, said body portion being divided into a pmr of sections by a longitudinal recess, said recess having a depth greater than the radius of the threaded body at the entering end of the fastener and providing an acute serrated cutting edge on one of said sections at the entering" extremity of the fastener which is adapted to cut away material when the fastener is turned within an unthreaded aperaure of a work piece, thread convolutions decreasing in external diameter toward the entering Yend of the fastener whereby to facilitate application thereof to an unthreaded aperture in a work piece.

5. A tapping fastener including a body portion provided with a thread, said body portion being divided into a pairof sections by a longitudinal recess, said recess having a depth greater than the radius of the threaded body at the entering .end thereof-and widening at the periphery of said body to provide an acute cutting edge on one of said sections at the entering extremity of the fastener which is .adapted to cut away material when the fastener is turned within an unthreaded aperture of a work piece. thread convolutions decreasing in external diameter toward lthe entering end of the fastener whereby to facilitate application thereof to an unthreaded aperture in a work piece.

6. A tapping fastener including a body portion provided with a thread, said body portion being' ldivided into a pair of sections by a longitudinal recess, the bottom of said recess being stepped and curved longitudinally of the screw and providing an acute cutting edge on the section ad-A jacent the shallower step of the recess whereby to enable the removal of material when the fastener is turned within an unthreaded aperture of a Work piece. 8. A tapping fastener including a body portion provided with a thread, said body portion at the entering end being divided into apair of sections by a longitudinal recess, said recess including communicating recess portions of dierent depths, the bottom surfaces of said recess portions being coaxially disposed, the section adjacent the shallower recess portion having an acute cutting edge.

9. A tapping fastenerincluding a body portion provided, with a thread, said body portion at the entering end being divided intoal pair of sections by 'a longitudinal recess, said recess including side walls of said recess providing rectangularv corners along the bottom of Asaid recess, the section adjacent the shallower recess portion having Y an acute cutting edge.

10. A tapping fastener including a body portion provided with a thread, said body portion 10 being divided into a pair of sections by a longitudinal recess, said recess comprising commlmieating recess portions, one'portionbeing deeper than the other, the side walls defining said recess portions being parallel and the bottom surface of each recess portion conforming with the arc of a circle and joining a companion side wail so as to provide a rectangular corner, the section adjacent the shallower recess portion having an acute cutting edge.

CARL G. OLSON. 

